This invention relates to an anticoagulant composition for use in a blood dialysis circuit, an air trap chamber device for the blood dialysis circuit and a method for blood dialysis in order to suppress blood coagulation and oxidation produced during blood dialysis due to contact of the blood with air.
In a venous air trap chamber, in which the pressure in the blood dialysis circuit is measured and the foreign matter, coagulated blood and air mixed into an adjustment circuit are removed, the blood is directly contacted with air. Since the blood is caused to flow at an increased rate into the air trap chamber, the blood surface is contacted with air so that the air is entrained into the blood to promote mixing and dissolution of the air into the blood frequently, resulting in the blood coagulation or activation and oxidation of the blood coagulating system. It is well known that the contact of blood with air tends to coagulate the blood. Besides, blood coagulation is promoted by the shear stress due to the blood stream. Besides, if air is contacted with the blood, the blood tends to be oxidized, that is the membrane of platelet, erythrocyte, leucocyte and lipoprotein tends to be oxidized. Oxidation is promoted by the presence of higher unsaturated fatty acids present in these membranes. Radicals from peroxide lipid produced by the oxidation leads to lesion in the endothelium of the blood vessel and to arterial sclerosis. Meanwhile, since the presence of an air layer in the air trap chamber is indispensable for pressure adjustment in the blood dialysis circuit, it is impossible in the current status of the art to remove air from the air trap chamber.
As pharmaceuticals for suppressing the blood coagulation during dialysis, heparin, low-molecular heparin, Nafamostat mesilate and have hitherto been employed. Above all, heparin is used predominantly because low-molecular heparin is more expensive.
However, it is not possible with the above pharmaceuticals to inhibit contact of the blood with air, while the blood oxidation cannot be inhibited even if blood coagulation may be inhibited. On the other hand, if used in a small amount, heparin is only poor in its ability in suppressing blood coagulation. For this reason, it is necessary to employ a large amount of heparin for prolonged time. As a result thereof, various side-effects, such as osteoporosis, hypersensitivity and lipid dysbolism due to increase in fatty acids in the blood are produced in a well-known manner. Besides, heparin has a longer intracorporeal half-life period and hence a longer hemostatic time so that it cannot be readily employed for a patient having a tendency towards hemorrhage or a patient treated with surgical operation. Although there is proposed, in conjunction with the use of heparin, a physical method of directly placing physiological saline on the blood in the air trap chamber for preventing the air and the blood from being contacted directly with each other, the practical effect is substantially nil because the air and the blood are mixed immediately. It is reported in Artificial Organs 14 Supp 14 edited by K. Ota and T. Agishi ICAOT press Cleveland 1991 (Japanese Laid-Open Patent Publication No. 2-119870) that Kitamoto et al. succeeded in floating tricaprylin on the blood in an air trap chamber to brake the contact between air and the blood.
However, since tricaprylin is used by itself, tricaprylin tends to be oxidized under the effect of a trace amount of metals in the air or blood, as a result of which the oxidized oil is brought into contact with the blood.
With the above-described conventional methods, it is not possible to prevent blood coagulation or oxidation in the air trap chamber effectively such that blood coagulation and adverse side-effects of the pharmaceuticals occur in the blood dialysis circuit. Besides, the quantity of the peroxide lipid in the blood is increased due to direct contact with air with the result that occurrence of lesions to the circulatory system such as arterial sclerosis as a complication of the patient treated with blood dialysis tends to be increased.